The present invention relates to a rotor arrangement for a slip ring assembly. Furthermore, the present invention relates to a rotary coupling arrangement comprising a slip ring assembly.
In the prior art, in particular in the field of coordinate measuring technology, it is customary to fit the sensors used to support structures which allow the sensors to move freely within a measurement area. The support structures are known in various forms, for example in the form of gantry constructions or else horizontal arm constructions. The support structures often have rotation axes which allow an arrangement, for example the sensor or else, for example, an intermediate rotary pivot joint, to rotate through up to 360°. Furthermore, fully freely rotatable rotation axes are used, in the case of which rotary movements can be performed through 360° several times. In addition to relatively large measurement areas, sensors of this kind are often also used in relatively small versions in the field of coordinate measuring technology, for example when bores or material features which are difficult to access need to be measured. In general, compact constructions of the support structures and of the rotation axes used are also desired in order that the support structure itself takes up as little measurement space as possible.
Various measuring systems, both of a tactile type and of an optical type, are known in the field of coordinate measuring technology. Furthermore, a distinction is made between measuring systems which sample individual points and those measuring devices which operate with so-called “scanning methods”. In scanning methods of this kind, —tactile or optical—sampling of a workpiece involves a particular path being followed on the workplace and a large number of measurement points being recorded along the path. It goes without saying that it is imperative, in particular in the case of scanning methods of this kind, for the position of the rotation axes and therefore of the measuring system to be able to be determined with a high degree of accuracy in order to be able to assign the corresponding exact spatial coordinates to the detected measurement points.
The use of slip ring assemblies is necessary in particular in the case of rotation axes or rotary joints which are intended to transmit rotary movements of 360° several times, so-called n×360 movements. Depending on the installation space available, it may also be the case here that a rotary movement beyond the slip ring assembly has to be transmitted starting from the sensor used to a measuring system for the rotary position. Problems in respect of hysteresis may occur in this case. However, hysteresis-free rotary movement and detection by a rotation position measuring system is absolutely essential, in particular in the field of coordinate measuring technology. Known slip rings are generally produced from plastic by injection molding. In the process, the contact rings used and the associated cables are encapsulated with plastic, wherein the plastic then provides the required insulation between the individual contact rings and cables and at the same time provides the shaft body of a rotor element of a slip ring assembly. However, a very large number of electrical contacts are currently required for modern sensors. If the number of cable elements to be provided is high in comparison to the installation space available, the problem may arise that a large portion of the shaft diameter available is taken up by the electrical cables themselves. As a result, only very little installation space which can be filled with plastic by injection molding remains, this leading to a very low torsional stiffness of the rotor shaft of the slip ring assembly. This can lead to twisting and even deformation of the slip ring rotor, and this may cause undesired problems in respect of hysteresis.
In particular in the case of highly accurate scannable rotation axes, in particular in the field of coordinate measuring technology, these problems can occur when transmission of the rotary movement beyond the slip ring assembly to a measuring system is required for structural or installation space reasons.
Although measuring systems for the rotation position generally have a dedicated bearing, they still have a certain resistance torque on the rotor of a slip ring assembly or on the entire rotation shaft which is coupled thereto. This also always causes corresponding twisting of the slip ring rotor given insufficient stiffness of the slip ring rotor, and this ultimately leads to the undesired hysteresis phenomena.
Although solutions without slip rings would avoid the undesired hysteresis phenomena, they generally do not allow the ability to rotate freely through rotation angles of more than 360°. Commercially available slip rings do allow rotary movements of more than 360° but the required torsional stiffness is not provided.
Corresponding problems to those in the case of coordinate measuring devices can also arise, for example, in the case of rotary tables or generally in the case of rotation axes or rotary joints in other applications which require compact designs and/or a low weight or moment of inertia.
Document DE 199 35 282 A1 describes a device for measuring a rotation angle, in which device the use of a slip ring is envisaged. Document DE 20 2009 017 928 U1 and document DE 10 2009 057 609 A1 describe a portable height gauge and scriber which likewise proposes a slip ring arrangement and the use of slip rings. Document DE 601 08 858 T2 describes a distance measuring means or a curve length measuring device in which an electrical coupling means can be formed by one or more slip rings and one or more brushes.
Document DE 201 10 415 U1 describes a checking apparatus for the measurement and/or dimensional tolerances of a rotationally symmetrical area of a workpiece, in which checking apparatus a feed and signal transmission device can be formed from one slip ring. Document DE 10 2008 028 403 A1 describes a displacement pickup for measuring the change in length of a sample, in which displacement pickup a friction coupling can be designed in the form of an adjustable spring/slip ring system. Document DE 31 33 477 C2 describes an apparatus for measuring the surface planarity of a plate. Document DD 249 523 A1 describes an apparatus for determining faults and marking faults in the case of non-conductive layers on electrically conductive material, which apparatus has a slip ring arrangement in this case. Furthermore, document DE 100 52 360 A1 describes an apparatus for measuring bores in a workpiece, in which apparatus a line section is guided in a slip ring body. Furthermore, document DE 295 19 611 U1 describes a cable-actuated length sensor, in particular for use in telescopic extension arms, which can have a slip ring arrangement.
However, in spite of this, there is also a need to solve the problems outlined above.
One object of the present invention is therefore to specify an improved rotor arrangement for a slip ring assembly or a rotary coupling arrangement, which rotor arrangement allows the hysteresis-free transmission of a rotary movement and is suitable, in particular, for use in small installation spaces for transmitting rotary movements of more than 360°.